Microelectronic devices are manufactured on silicon wafers, gallium arsenide wafers, and other types of semiconductor substrates. The semiconductor substrates generally have an epitaxial layer with discrete regions were specific types of atoms have been incorporated to impart the desired conductivity to the discrete regions. A typical ion implantation procedure involves constructing a pattern across the surface of the substrate using photolithography processes, and then implanting exact concentrations of the atoms into the epitaxial layer. The workpieces are then stored in cassettes that hold a plurality of similar substrates for further processing in tools at different locations throughout a facility.
One problem with manufacturing microelectronic devices is that some cassettes may be mislabeled or the workpieces may be loaded into the wrong cassette. For example, because semiconductor device manufacturers typically process many different types of products with different dopants at the same facility, substrates can be inadvertently loaded into the wrong cassettes or otherwise misplaced. As a result, such substrates will be processed incorrectly in subsequent procedures and likely ruined after having been processed through very expensive photolithographic and ion implantation procedures.
To reduce such errors, the semiconductor manufactures may periodically identify the type of dopant in a semiconductor substrate by measuring the conductivity and mobility of the particular substrate. This process includes mechanically contacting the substrate with electrical contacts and passing an electrical current through the substrate. Although this procedure correctly identifies the type of dopant, mechanically contacting the substrate with the electrical contacts is not desirable. First, the electrical contacts can introduce or generate small particles that can contaminate the substrate and affect subsequent processes. Second, this process is time-consuming and reduces the throughput of manufacturing semiconductor devices. Therefore, there is a need to quickly determine the type of dopant in a semiconductor substrate without contaminating the workpieces.